Generally, an exhaust gas exhausted through an exhaust manifold from an engine is led to a catalytic converter formed on an exhaust pipe and is purified. After that, noise of the exhaust gas is reduced when the exhaust gas passes through a muffler and is exhausted to the air through a tail pipe.
A selective catalytic reduction (SCR) converter is one type of such catalytic converters.
The SCR means that reducing agents such as urea, ammonia, carbon monoxide and hydrocarbon (HC) react better with nitrogen oxide than oxygen.
An exhaust system of a vehicle provided with the SCR converter includes a urea tank and a dosing module. The dosing module injects the reducing agents such as the urea into the exhaust gas passing through the exhaust pipe. Thereby, the SCR converter can reduce the nitrogen oxide efficiently.
However, if the urea is insufficient in the urea tank, nitrogen oxide in the exhaust gas cannot be sufficiently purified and is exhausted to the exterior even though the SCR converter is mounted at the vehicle. Therefore, regulations demand that means for inducing a driver to replenish the urea if the urea in the urea tank is insufficient should be mounted at the vehicle. This is called a driver inducement.
If a urea level in the urea tank is lower than a predetermined level, a conventional driver inducement method induces a driver to replenish the urea. However, a urea consumption is closely related to an actual operating state of the vehicle, particularly to a vehicle speed. Therefore, even though the vehicle can run hundreds of kilometers, driver inducement needs to be performed because of a low urea level.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.